In the manufacture of small appliances, such as power toothbrushes, it is important that the drive assembly portion thereof be in precise physical alignment relative to the driven member which, for instance, could be a pivoted arm on which a workpiece (a brushhead) is mounted. In a typical known approach, a carrier is assembled with a number of internal parts of the appliance mounted thereon. The carrier is then installed into a handle housing, typically from a bottom (proximal) end thereof, over which is secured a cover. The driven member is mounted to the other (distal) end of the handle housing. Reliable alignment of the driving assembly with the driven member is thus often difficult because the interface between the driving assembly and the driven member is at the opposite end of the handle housing from the point of installation of the driving assembly.
Misalignment, due to relative sideways or even rotational movement between the driving assembly and the driven element readily occurs. The interface between the driving assembly and the driven element is typically part of the housing, thus making the housing a critical element in the proper operation of the appliance. A spring or other part is often used to hold the driving assembly to the interface, but this adds to the overall expense, size and complexity of the device. Due to manufacturing and tooling considerations, this bottom loading approach also requires that the housing be larger at the bottom than at the top, which is undesirable from an aesthetic and ergonomic standpoint.
In another aspect of the invention, a driving assembly may include an electromagnet having a center core winding. The core member which holds the winding, referred to as a bobbin, is secured at one end to the electromagnet frame, which includes the electrical pin connections/terminals to the coil winding and the battery, while the other end is secured to or is a part of a mounting/interface element which is secured to the handle portion of the appliance and to which is secured a head portion of the device.
The mounting element and the portion of the bobbin secured thereto is exposed to the operating environment of the appliance; e.g. toothpaste and water or other dentifrices for a power toothbrush. The portion of the bobbin secured to the mounting element thus must also be of a material which can stand exposure to the operating environment of the appliance, such as toothpaste and water for a power toothbrush, as well as being attractive to the consumer including the capability of being colored.
The portion of the bobbin attached to or part of the frame must be heat-resistant to withstand the elevated temperatures encountered during soldering of the wire terminations from the core winding to the pin connections which also receive wire connections from the battery. This portion of the bobbin must also be high strength, to withstand the coil winding process.
Unfortunately, no single material has all of the above capabilities/characteristics. Hence, there have been design compromises with respect to the construction of winding bobbins in power toothbrushes in particular, either in the design of the bobbin itself and/or its relationship with the other portions of the drive assembly. Further, a single part requires a complex and hence expensive manufacturing tool. In this aspect of the invention, it is desirable to have a bobbin assembly which satisfies all of the above-described requirements.